Two-component coating agent

ABSTRACT

The invention concerns a two-component coating agent with a) a water dilutable binder component of a polyester resin base and/or polyacrylate resin base, whereby the polyester and/or polyacrylate resin has a content of hydroxyl groups of 2.5 to 8% by weight OH and b) an aqueous organic polyisocyanate component of at least one polyisocyanate with free isocyanate groups which is prepared ready for use for a limited time by the stirring of the polyisocyanate component b) into the binder component a) and hardens by cross-linking of the binder component with the polyisocyanate to the binder components according to the invention are provided as aqueous emulsions of a water insoluble carboxylate-free and sulfanate-free polyester resin and/or polyacrylate resin, whereby the emulsion is produced with the aid of an emulsifier added to the polyester or polyacrylate resin. The subject of the invention is, further, a process for producing the water-dilutable binder component a).

DESCRIPTION

The invention relates to a two-component coating agent with

a) a water-dilutable binder component based upon polyester resin and/orpolyacrylate resin whereby the polyester resin and/or polyacrylate resinhas a hydroxyl group content of 2.5 to 8% by weight OH, and

b) a liquid organic polyisocyanate component of at least onepolyisocyanate with free isocyanate groups,

which by stirring of the polyisocyanate component b) into the bindercomponent a) is prepared for use for a limited time and hardens bycross-linking of the binder component with the polyisocyanate.

The water dilutable two-component coating agent known from EP 0 358 979A2, from which the invention starts, contains as the binder component,polymers with sulfonate groups and/or carboxylate groups. In theproduction of these polymers, monomers are used which contain carboxylicacid and/or sulfonic acid groups. By neutralization of the acid groupswith inorganic bases or amines, a water solubility or dispersibility ofthe polymer is achieved. It has been found, however, that theneutralizing agent had a negative influence upon the water resistance,the weathering resistance, the corrosion prevention and the drop time ofthe coating agent.

Further from DE-OS 15 95 685 a process for producing modified aqueouspolymer dispersions is known, in which an aqueous dispersion of polymersor mixed polymers with a reaction product having a free NCO group ofhigher molecular weight in a compound with at least two active hydrogenatoms can be reacted with an excess of polyisocyanate. The reactionproduct having the free NCO groups is stirred into the aqueous polymerdispersion. The mixture can stand for a period of three to ten daysuntil the content of free NCO groups drops to zero. The result is astable chemically fully reacted dispersion which can be diluted withwater and used as a coating agent and impregnating agent, preferably asa finishing (sizing) agent in the textile field, usable as a singlecomponent. For the development of chemically cross-linking two componentcoating agents, these teachings have not been effective.

The invention has as its object an aqueous two-component coating agentof the type described initially which affords good water resistance andweathering resistance.

To achieve this object, the invention teaches that the binder componentsbe provided as aqueous emulsions of a water-insoluble carboxylate-freeand sulfonate-free polyester and/or polyacrylate resin, whereby theemulsions are formed by addition of an emulsifier to the polyester orpolyacrylate resin. The hydroxyl group content of the polyester resin orpolyacrylate resin is preferably in the range of 4.5 to 8% by weight OH.The NCO/OH equivalents ratio can be set in the range of 0.8:1 to 3:1 andpreferably lies at 1.5:1. The subject of the invention is also a methodof making the water-dilutable binder components for a two-componentcoating agent hardenable with polyisocyanate as previously described.

According to the invention, polyester resins and/or polyacrylate resinsare used as binder components which are dissolved in organic solvents asare known from solvent-containing lacquer technology. The solids contentlies in the range of 70 to 100 weight %, preferably between 80 and 90weight %, the balance organic solvent. The polyester resins orpolyacrylate resins have a viscosity of 1000 to 11000 mPa s/23° C. asmeasured by rotation viscosimeter. The polyester resin and/orpolyacrylate resins are introduced in their water insoluble form,carboxylate-free and sulfonate-free, in aqueous emulsions whereby theemulsions are produced with the aid of emulsifiers added to thepolyester resins and/or polyacrylate resins. As emulsifiers,anionically-active, nonionic and cationically-active emulsifiers aresuitable as are customarily used for the production of synthetic resinsand binders by polymerization and for example as basis emulsifiers forall kinds of emulsion polymerization or as coemulsifiers for thestabilization of polymer dispersions.

The amounts of emulsifier added lie between 0.1 to 10 weight % basedupon the solvent-containing form of the polyester resin or polyacrylateresin. After addition of the emulsifier to the polyester resin orpolyacrylate resin, a dilution is effected with water so that a stableemulsion results with a solids content (content of polyester resinand/or polyacrylate resin) of preferably 25 to 60% by weight. Forproducing the ready-for-use coating agent, the polyisocyanate componentsare stirred into the described emulsion, whereby the polyisocyanatecomponents are emulsified. The content of free NCO groups of thepolyisocyanate component is in the range of 8 to 32% by weight basedupon the solids of the component. The viscosity amounts to 40 to 9000mPa s/23° C. (measured in the rotation viscosimeter). Where required,small amounts of an inert solvent can be incorporated in thepolyisocyanate component to improve the incorporation of thepolyisocyanate component b) in the binder component a). The result ishigh quality cross-linked films which are not inferior with respect totheir characteristics to the coatings known in the organic lacquerfield. Presently, the emulsifiers have no negative effect upon the filmcharacteristics.

The two-component coating contained according to the invention issuitable for coatings of all kinds, impregnation and painting. It isself-understood that the usual auxiliaries and additives of lacquertechnology can be added to the binder component. These includeespecially defoaming agents, flow enhancers, pigments,dispersion-promotion agents for pigment distribution and the like.

Table 1 shows in Examples A to F without limitation of the teachingsaccording to the invention, suitable compositions for a binder componentwhich can be introduced as a reaction component of a two-componentcoating agent. As a polyacrylate resin, a resin (a Johncryl 507, Johnsonpolymer) dissolved in butylacetate known from solvent-containing lacquerpractice, is introduced, whereby the solids content is previouslyconcentrated to 85 weight %, balance solvent, by solvent distillation.As the polyester resin, there is also used a polyester resin known fromthe solvent-containing lacquer practice, i.e. a resin (Synthoester HD170, Synthopol Chemie) dissolved in butyl acetate in which the solidscontent amounted to 80% by weight, balance solvent.Commercially-available emulsifiers are added to the polyester resin orpoly-acrylate resin as indicated in the given amounts:arylpolyglycolether (emulsifier WNS, Bayer), 2,4,7,9-tetramethyl-5decin-4,7-diol (SURFYNOL 104, Air Products), sorbitan ester (DISPONILSMO, Henkel) and ricinus oil ethoxylate.

Thereafter the emulsion can be adjusted as required for the purposes ofuse by the addition of the usual auxiliaries and additives of lacquertechnology, especially pigments and defoaming agents. Also a furtherdilution with water can be effected.

The binder components are available in the form of an aqueous emulsion.Into the emulsion a liquid organic polyisocyonate component with atleast one polyisocyanate with free isocyanate groups is emulsifyinglystirred. The mixture is ready for use for a limited time and hardenswith a cross-linking reaction. High quality cross-linked films result asare known from organic lacquer practice. The water resistance of thecoating agent is provided already after four hours.

EXAMPLE 1

From the aqueous emulsion A given in Table 1, a binder component of thefollowing composition is produced:

48.0 parts emulsion A

28.0 parts titanium dioxide rutile (R KB-4, Bayer AG)

0.2 parts defoamer (Byk 034, the firm Byk Wesel).

The mixture is predispersed with a dissolver, then homogenized for 15minutes in a bead mill and then further diluted with 23.8 parts ofdistilled water.

After addition of 15.9 parts polyisocyanate (Tolunate HDT 90, RhonePoulenc) one obtains a two-component lacquer with a working duration inexcess of three hours.

EXAMPLE 2

The aqueous emulsion C given in Table 1 is worked up to a bindercomponent with the following composition:

52.0 parts emulsion C

28.0 parts titanium dioxide rutile® KG-4, Bayer AG)

0.1 parts defoamer (Byk 034 of the firm Byk Wesel)

0.1 parts wetting agent (Fluorad FC 129, 3M).

The mixture was predispersed with a dissolver, then homogenized for 15minutes in a bead mill and finally diluted with 19.8 parts of distilledwater.

After the addition of 19.3 parts of polyisocyanate (Desmodur VP LS 2550,Bayer AG), one obtains a two-component lacquer workable for over fivehours.

The lacquers described in Examples 1 and 2 are brought with distilledwater to a run-out time of 45 sec according to German IndustrialStandard 53211-4 and are applied in a coating thickness of 50 μm toglass plates. The hardened lacquer has the characteristics given inTable 2.

TABLE 1 A B C D E F Polyacrylate Resin 85% 69 59 49 29 10 ButylacetateOH-Content 4.5% Polyester Resin 80% — 10 69 20 40 50 ButylacetateOH-Content 5% Arylpolyglycol 1 1 1 1 ether 2, 4, 7, 9-Tetra 0.3 0.3 0.30.3 0.5 0.5 methyl-5-decine- 4,7-Diol Sorbitan ester 0.5 0.5 Ricinus oil0.8 0.8 2.5 2.8 ethoxylate Distilled water 29.2 29.2 28.9 28.9 28 27.7

TABLE 2 Characteristics Example 1 Example 2 Brightness according to 88%79% German Industrial Standard 67530 (incidence angle 20°) Pendulumhardness according to 44 sec 48 sec German Industrial Standard 53157measured at room temperature after 1 day measured at room temperature 93sec 98 sec 7 days Solvent resistance after 14 days, Good Good measuredat room temperature Super gasoline lead-free Methoxypropylacetate GoodGood Test gasoline Very Good Very Good

What is claimed is:
 1. A process for producing a water-dilutable binder,having hydroxyl groups and after an addition of a liquid organicpolyisocyanate component with free NCO-groups in an amount whichcorresponds to a proportion of NCO/OH of 0.8:1 to 3:1, which is ready tobe used as an organic lacquer coating agent and which after beingapplied to a substrate hardens into a hard film due to crosslinkingreactions, consisting essentially of the following steps: a)concentrating a binder which consists of a non-water-soluble,carboxylate and sulfonate free polyester resin and/or polyacrylate resinwith a content of hydroxyl groups of 2.5 to 8% by weight OH and anorganic solvent to a content of solids of 80 to 90% by weight, thebalance being the organic solvent to form a solvent-containing polyesterand/or polyacrylate resin; b) adding to the concentrate produced in stepa) an emulsifier in an amount of 0.1 to 10% by weight of thesolvent-containing polyester and/or polyacrylate resin; and c)subsequently to step (b), blending water with the solvent-containingpolyester and/or polyacrylate resin to create the water-dilutable binderas a storage-stable emulsion, capable of blending with thepolyisocyanate component with free NCO groups prior to use.
 2. Theprocess according to claim 1, whereby pigments are added to theemulsion.
 3. The process according to claim 1, whereby the emulsion isfurther diluted with water prior to blending with the polyisocyanatecomponent.
 4. The process according to claim 1 wherein thenon-water-soluble, carboxylate and sulfonate free polyester resin and/orpolyacrylate resin with a content of hydroxyl groups has an OH groupcontent of 4.5 to 8% by weight.